This file is over 20k lines long, and 400kB

It is nested over 10 levels deep in many places

There is no naming consistency. The original file used BEM, but now it switches randomly between whatever the devs felt like at the time. There are random contractions all over the place (eg, a parent container might have the class payment-items, but the children are p-item)

There is no style consistency. It switches randomly between kebab case, camel case, snake case, a mix of kebab and snake case (!!) or no case at all (just one long word with no separators). A parent element might use one case, but then the child element will use a different case for the exact same term